Are there any adjustments (preload specifically) that need to be considered before buying a new spring? If you can't even compress it an inch, it sounds like perhaps you need to back off on the preload a bit. If you bought the bike from an LBS, take it back and have them make it right for you. That's what you paid them for. If not, you'll need to read up on the fork and do the adjustments yourself. It's not hard at all.
with a three spring option as with the Dart the ranges are pretty broad. The fork comes stock with a medium spring intended for riders in the 150 to 180lb, or possibly higher, range. The soft spring will be suitable for riders from 150lbs and below. The range between soft, medium and heavy is usually right at 30lbs (+ or -) of body weight. Some times as low as 20lbs of range, but that usually dictates at least one additional spring. So assuming a 30lb range I don't think you'll have any problems with the soft spring. Even at 20lbs between spring ranges the soft would still be right where you need to be. I've set up enough RS coil forks for light weight riders, and you need a soft spring. I'm amazed your LBS didn't order this for you right off the bat! Suspension set up is all part of bike setup and fit.
Anyway, order up the soft spring set, it's definately what you need and it definately won't be too soft for you.
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